At present, an ink ribbon used by a dot matrix printer generally consists of a ribbon cassette and a ribbon winding inside the ribbon cassette. Generally, two colors, i.e., black and red are provided side by side in the direction of the width of the ribbon. Through adapting the different-colored ribbon to a position opposite to a print head by swing the ribbon cassette and then forming color image or text by hitting ink on the ribbon of the ink ribbon onto a print medium with print needles on the print head, a color printing is implemented.
At present, a printer is disclosed in a Chinese Patent entitled “A PRINTER” (Application No. 00102697.6), which includes a main body having an ink ribbon cassette and an ink ribbon cassette lifting/lowering mechanism, with the latter detachably mounted on a side portion of a machine frame. The ink ribbon cassette lifting/lowering mechanism includes a gear mechanism for transmitting rotation of a driving shaft mounted on the frame to a bracket detachably mounted on the frame, a cam mechanism for lifting and lowering the ink ribbon cassette, a clutch for selectively transmitting rotation of the gear mechanism to the cam mechanism, and a actuator for connecting and disconnecting the clutch. Therefore, a monochrome printer is possibly to be used as a multi color printer and the rotating speed of the cam can be set freely. Although in this solution a monochrome printer can be used as a multi color printer, there are some drawbacks, i.e., when a monochrome printer is used as a multi color printer the structure of the ink ribbon cassette lifting/lowering mechanism will be complicated due to the need to provide the cam mechanism, the clutch and the actuator, resulting in higher costs for producing and controlling.
In addition, a technical solution disclosed in a US patent entitled “INK RIBBON SHIFTING PRINTER” (Publication No. U.S. Pat. No. 5,468,078) includes that the movement region of the print head is divided into three regions, i.e., one printing region and two non-printing regions, wherein, the two non-printing regions are respectively located at two ends of the printing region, an ink ribbon raising device and an ink ribbon releasing device are disposed respectively at the endpoints of the two non-printing regions, in which the ink ribbon raising device is used for adjusting the relative position of the print head and the color of the ink ribbon such that the ink ribbon is disposed in a desirable color for printing, while the ink ribbon releasing device is used for releasing the ink ribbon to an original height.
This method involves too many regions (three regions), and meanwhile, each time an ink ribbon shifting takes place, the print head needs to pass through the whole region, i.e., the print head needs to move to a first non-printing region at an end in a movement direction for ink ribbon shifting, if it is to be reset, the print head needs to move to a second non-printing region at the other end for ink ribbon releasing. In this way, the print head needs to move too long a track to complete a set of shifting and releasing. At the same time, two devices, i.e., an ink ribbon raising device and an ink ribbon releasing device, need to be provided to perform the shifting and resetting of the ink ribbon in the prior art respectively. The printer provided by this prior art involves too many devices, and its structure is relatively complicated, so that it is much difficult to develop such prior art and the costs of electrics and controlling are too high.